ControlLogix CPU Usage Varying

aufisherman

Member
Join Date
Apr 2016
Location
Pensacola
Posts
16
Hello,

I am trying to perform the new Rockwell PlantPAx Verification checklist thing.

If execution time is not varying on my tasks, but the CPU usage is varying greatly (20% to 70%) what could be the culprit?

I see that there is an issue, but I cannot find any information on specifically what to look for inside my routines to identify the source of this varying cpu usage.

Any thoughts?


Thanks!
 
Are you using a lot of timed tasks? CPU usage could be low when not doing an active task, but high when doing so? Not sure how long of a time that "usage" is averaged over.
 
This is not batch. It is a continuous process and we are using periodic tasks. My 1000ms task that has all of IO and regulatory control FBDs is the one that is varying from 50-95% cpu usage while scan time varys between 170,000-220,000 microseconds.
 
They are periodic tasks. The culprit is a 1000ms periodic task that has all the IO and regulatory control FBDs. The scan time will hover between 170,000-220,000 microseconds. Sometimes the scan time will stay the same while the CPU usage just climbs from 50% to 99%
 
Haha. This is one of the only "full DCS" implementations of ControlLogix that I have really worked on. The controllers are being used for process control.

The process library objects that are used for a PlantPAx implementation are very heavy on useless stuff you never need so a lot of overhead.
 
That's a brutal scan time, but makes sense with a big PAx program. Just curious, what processor are you running and about how much I/O?
 

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